Spoiler (aeronautics)

Most often, spoilers are hinged plates on the top surface of a wing that can be extended upward into the airflow to spoil the streamline flow.

However, the most gain comes as the spoilers cause a dramatic loss of lift and hence the weight of the aircraft is transferred from the wings to the undercarriage, allowing the wheels to be mechanically braked with less tendency to skid.

Some aircraft use spoilers in combination with or in lieu of ailerons for roll control, primarily to reduce adverse yaw when rudder input is limited by higher speeds.

In the case of a spoileron, in order for it to be used as a control surface, it is raised on one wing only, thus decreasing lift and increasing drag, causing roll and yaw.

Eliminating dedicated ailerons also avoids the problem of control reversal and allows flaps to occupy a greater portion of the wing trailing edge.

On landing approach "automatic" is selected and, on touchdown, a sensor called a weight-on-wheels switch signals the lift dumpers to be raised.

The British Aerospace 146 is fitted with particularly wide-span spoilers to generate additional drag and make reverse thrust unnecessary.

A number of accidents have been caused either by inadvertently deploying lift dumpers on landing approach, or forgetting to set them to "automatic".